In many consumer imaging applications like flat-bed and hand-held scanners, an image coming from one or more charge coupled device (CCD) sensors must be processed in order to compensate for the nonuniform illumination of the subject. In a typical application, three COD sensors are used (one for each of the primary colors red, green and blue (RGB)) to scan the subject on a line-by-line basis. Typically, the sensitivity of each of these sensors is different. Also, the sensitivity of each pixel within one of the line sensors may be different. Finally, because of constraints in mechanical construction and optics of the scanner bed itself, the illumination of the subject is not constant across a line.
To obtain a correct two-dimensional picture out of the CCD signals, two kinds of correction must be performed: global gain and offset correction to account for the difference in sensitivity between red, green and blue sensors, and pixel-by pixel correction to account for the difference in illumination (or sensitivity) within one line.
Prior attempts have utilized scaling or offset correction on individual pixels in the analog domain. This has proved ineffective primarily due to a lack of sensitive analog processing. Better methods are needed to improve resolution.
It is accordingly an object of this invention to provide an apparatus and method for improving resolution in CCD scanning.
Other objects and benefits of the invention will be apparent to those of ordinary skill in the art having the benefit of the description and drawings following herein.